In recent years, a number of studies in Russia and abroad was completed with the aim of decreasing pressure fluctuations and losses in blade cascades by controlling the unsteady interactions of blade rows (known as “clocking effect”) [1–4]. Tests of individual stages demonstrated that the clocking effect is responsible for 1.5–2.0% in efficiency and 50% in pressure fluctuations . This paper presents the results of experimental and theoretical studies of the clocking effect on gas-dynamic characteristics of a high-loaded two-stage compressor simulating the first two stages of HPC for an advanced engine. The compressor is designed with the help of up-to-date 1D, 2D and 3D direct and inverse problem solutions and distinguished by high aerodynamic loads of stages with πk=3.7 total pressure ratio, 17% stall margin and 88% adiabatic efficiency at Ncor=88% rotational speed that was demonstrated experimentally .
The compressor was tested at CIAM’s C-3 test facility in the assembly with d=0.5, 0.75, 1.0-mm tip clearance in both rotors (relative clearance in first stage 4.6·10−3; 6.9·10−3; 9.2·10−3 and relative clearance in second stage 9.1·10−3; 13.7·10−3; 18.3·10−3). When tested, clocking effects were checked up for separate and simultaneous changes in clocking positions of stator and rotor blade rows. Indications of a blade tip-timing system and pressure pulsation sensors were used as experimental data. Earlier, it was shown that physics of the rotor clocking is a wake interaction which modifies the behavior of a boundary layer in Rotor 2 blades. This work studies the mechanism of rotor clocking in combination with changes in angular position of Rotor 2 blades due to interactions with Rotor 1 wakes. Tests showed that changes in the clocking position of the rotor with a multiple number of Rotor 1 and Rotor 2 blades affected the static position of Rotor 2 blades causing re-position of the blades depending on the rotor clocking-position. To confirm this result, 3D unsteady aerodynamic calculation was completed with the help of NUMECA software package simulating one of the test points. This work presents the calculated and experimental data showing that vortex wakes from Rotor 1 blades extend downstream, reach Rotor 2 and cause a variable aerodynamic load and a variable blade pitch.